How can you keyframe textures changing?
There are multiple options:


you can animate the nodes in the material itself to mix multiple textures (animate factor of Color > Mix node):


put all your textures into a single image (image atlas). Then you can use the UV Warp modifier to translate the UV coordinates across the image atlas.

To control the modifier:


create an armature rig and animate the bone positions (as shown in this UV Warp tutorial)
create an integer custom property and use it to drive the bone/empty location in single axis. The image atlas should be an image strip with equally spaced images in this case. Then you keyframe the integer property that switches all the textures.